Green Comet

Corona

Posted on 2014-07-18 by arjaybe

Corona diagram

All images, except where noted, credit Wiebke Salzmann CC-BY-SA. Click images for larger versions.

Cloud of the Day – Corona

Here is a meteorological phenomenon that is often misnamed “halo.” A corona is similar to a halo in that they both form rings around the Sun and Moon. The Sun’s corona (the one formed in Earth’s atmosphere, not the one around the actual Sun) is hard to see because the Sun is so bright. A corona is a more subtle effect and needs the more muted light of the Moon to really show itself.

While haloes result from the light being refracted by ice crystals high in the atmosphere, coronae are caused by the diffraction of light scattered by particles – water droplets, ice crystals, dust motes, etc – in the lower atmosphere. A corona can also form on a foggy window pane. Haloes have fixed dimensions, calculable from the known refractive index of ice. Coronae come in various sizes due to the variability in the size of the light-scattering particles. Smaller droplets make larger coronae. In addition to the light scattered from the surface of the particle, small contributions to the corona are made by light that reflects directly off the droplet, or passes through it.

Corona around street lamps through an aspirated window pane.

Corona around street lamp through an aspirated window pane.

$Artificial corona around LED lamps of different colors, created with lycopodium spores. As can be seen the diffraction rings of red light have a greater radius than those of blue light.$

Artificial corona around LED lamps of different colors, created with lycopodium spores. As can be seen the diffraction rings of red light have a greater radius than those of blue light.

Image credit - Florian Marquardt - CC-BY-SA

Interference patterns – Florian Marquardt – CC-BY-SA

Lisa Harbinson – CC-BY-SA 2024

A classic corona consists of a bright aureole in the center, with one or more colorful rings around it. For the sharpest coronae, the droplets must be all close to the same size, so the interference pattern in the light can be well defined. It is constructive and destructive interference among the scattered light waves, where they add to make bright regions and subtract to make dark regions, that make the alternating rings of bright and dark.

rjb

Posted in Uncategorized | Tagged cloud of the day, clouds, light, weather | 12 Comments

Pery Burge

Posted on 2014-07-12 by arjaybe

Photo credit – Pery Burge – click for larger image

Pery Burge died in 2013, but she left behind a collection of beautiful photographs. Asked how she generated her photographs, Pery Burge said, “I place ink in water, which I photograph . . .” Trust me, there’s a lot more to it than that. In her Artist’s Statement, she said, “In 2011, I began to work with glass and light . . .” That series of photos she called “Lightscapes.” She also has a series called “Smoke.” There’s a series called “Lab Images,” one called “Bubblespreads,” and one containing her personal selections, and many more besides. Finally, you can see tons of her photos on her flickr photostream.

Her website, “Chronoscapes,” has a final journal entry entitled “Pery Burge,” written by a friend shortly after her death. In a sad irony, her own final entry was entitled “Looking Forward to 2013.”

Pery Burge died too young, but she left beauty behind.

rjb